A solid-state imaging device 900 shown in FIG. 16 is an example of conventional solid-state imaging devices. The solid-state imaging device 900 has a pixel region where pixels are two-dimensionally arrayed, and a peripheral region surrounding the pixel region. The solid-state imaging device 900 also has: a P-type (first conductivity type) well region 910; an N-type (second conductivity type) photodiodes 912, which are photoelectric converters formed within the well region 910; P+-type (first conductivity type with a high concentration of impurities) doped regions 914, which are formed within the well region 910; insulating films 920 and 930, which are layered on the well region 910; and light-shielding films 940, which are made of metal and are formed on the regions of the insulating film 930 respectively corresponding to the doped regions 914. Although not depicted in the drawing, a reset transistor and an amplifying transistor are formed within the well region 910.
Here, if the well region 910 is charged from the peripheral region of the solid-state imaging device 900, the electric potential of the well region 910 could be non-uniform due to the resistance of the well region 910. Specifically, the central region of the well region 910 could have a lower electric potential than the peripheral region. The well region 910 serves as the back gate of the transistors. Therefore, if the electric potentials of the pixels in the well region 910 are different, the maximum amount of electric charge that can be accumulated in the photodiodes 912 could vary among the pixels even with the same amount of incident light. Consequently, the output signals could be different among the pixels, and shading could occur in the image. In order to prevent this problem, in the solid-state imaging device 900, the light-shielding film 940 is held at a fixed potential, and the doped regions 914 and the light-shielding films 940 are electrically connected via well contact regions 922. Thus, the electric potential of the well region 910 is made stable at every pixel.
There is another problem that electrical charge generated in the well region 910 due to thermal excitation could cause dark current. In order to prevent the dark current from entering the photodiodes 912, the P-type (first conductivity type) well region 910 is formed on an N-type (second conductivity type) substrate connected to a power supply voltage, for example. When the N-type (second conductivity type) substrate has a higher electric potential than the well region 910, the dark current generated in the well region 910 flows out to the substrate having a higher electric potential than the well region 910.